US3736556A - Method and apparatus for increasing seismic signal-to-noise ratio - Google Patents

Method and apparatus for increasing seismic signal-to-noise ratio Download PDF

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Publication number
US3736556A
US3736556A US00178654A US3736556DA US3736556A US 3736556 A US3736556 A US 3736556A US 00178654 A US00178654 A US 00178654A US 3736556D A US3736556D A US 3736556DA US 3736556 A US3736556 A US 3736556A
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signal
geophone
time
function
multiplying
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F Barr
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Halliburton Geophysical Services Inc
PETTY GEOPHYSICAL ENG CO
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PETTY GEOPHYSICAL ENG CO
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
    • G01V1/28—Processing seismic data, e.g. for interpretation or for event detection
    • G01V1/284—Application of the shear wave component and/or several components of the seismic signal

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  • ABSTRACT An improved technique for enhancing the signal-tonoise ratio in the automatic processing of seismic data is provided according to the present invention.
  • Signals from horizontally and vertically oriented geophones, representing *two' functions of time, are separately recorded.
  • the product of these two signals is formed as a signal representative of a third function of time.
  • the product signal thus formed is then used in various ways as an enhancement function signal, to attenuate noise components and enhance seismic signal components.
  • One technique for utilizing the enhancement function signal involves half-wave rectifying the enhancement function signal and then multiplying the rectified signal by the original signal from thevertically oriented geophone.
  • Another technique involves using the enhancement function signal to produce a gating signal to cancel the original output signal from the vertically oriented geophone whenever the enhancement function signal is other than negative.
  • the present invention relates generally to seismic surveying and more particularly to the automatic pro cessing of information in the form of seismic signals.
  • seismic signal means a signal representative of a compressional wave.
  • the present invention contemplates the use of a geophone oriented to receive principally energy from a horizontal direction and a geophone oriented to receive principally energy from a vertical direction, placed near each other on the surface of the earth.
  • the terms horizontal geophone” and vertical geophone refer respectively to geophones so oriented.
  • the geophones receive waves caused by an explosioi or disturbance at another point, either on the surface of the earth, or above or below the surface.
  • the output signals from the horizontal and vertical geophones are recorded as separate channels on an appropriate seismic-signal recording device, producing signals representative of two functions of time.
  • the signal-enhancement-function signal is then used, in any of a variety of ways, with the signal representative of a second function of time, to produce a signal representative of a fourth function of time. This signal is then filtered to attenuate undesired frequencies in which seismic signals have been enhanced and seismic noise has been attenuated.
  • FIG. 1 of the drawings is a general representation of the subsurface regions of the earth which are of interest.
  • FIG. 2 is a side view of geophones and their mounting, which may be utilized in a preferred embodiment of the invention.
  • FIG. 3 is a plan view of said geophones.
  • FIG. 4 is a schematic representation of one form of apparatus which may be used in carrying out the present invention.
  • FIG. 5 is a schematic representation of another form of apparatus which may be used in carrying out the present invention.
  • FIG. 1 a set of rectangular coordinate axes x,y,z, intersect at point P.
  • the axes x and y define a horizontal plane to which the surface of the earth approximately conforms for short distances. Assuming that a shot point or other source of seismic energy is located somewhere along the x axis, the following subsurface regions may be defined, as shown in FIG. 1:
  • Region 1 is the space within the cone surface described by an angle y, sin (Bled from the vertical or z axis, where a is the velocity of propagation of compression waves in the earth, and B is the velocity of propagation of shear waves in the earth.
  • Region 2 is the space between region I and the cone surface described by an angle of 45 from the vertical or z axis.
  • Region 3 is the space outside regions 1 and 2 and below the surface of the earth.
  • FIG. 1 Also pictured in FIG. 1 are various waves arriving at point P. These are:
  • matched horizontal and vertical units model No. GSC-l 1D, available from Geo Space Corporation, Houston, Tex., may be employed. It is desir-able that the geophones used be, as nearly as possible, a matched pair.
  • the geophones 4 and 5 are mounted on a platform comprising three sections 7, 8 and 9. Section 7, the
  • center section is horizontal and is designed for the readyfastening thereto of support spikes 6, in the conventional manner well known to persons skilled in the art.
  • cant section 8 of the platform by a small angle to the horizontal plane, for example, and to cant section 9 by the same angle to the vertical plane, so that the sensitivity axes of geophones 4 and 5 are maintained perpendicular to each other.
  • An imaginary extension of the sensitivity axis of geophone 4 should include a shot point from which seismic waves originate, as shown in FIG. 2.
  • leads 10 and 11 extend from the horizontal and vertical geophones 4 and 5 respectively, to conduct the output signals thereof for processing in accordance with the invention.
  • FIGS. 2 and 3 The assembly of FIGS. 2 and 3 is placed on the surface of the earth.
  • the geophones 4 and 5 are located at a single point, such as point P in FIG. 1.
  • the vertical and horizontal geophone output signals resulting from the arrival of the previously mentioned waves at point P may be expressed as v.0) ('Yz) os more) +Ft vz oos MUM) +H oos 0.0) i lm-tf l m ozmw, a)
  • V (2) V, (t) is negative or decreasing in the presence of the undesired signals s(t), "10( and "28( 3. Since each frequency component of a function of time f(t) is in quadrature with ea ch frequency component of lf(t) i, ,f(t) lf(i) iorlz is a much smaller function than 1 (t).
  • the resulting product signal V, (r) V, (I) may be modified and used to operate upon V, (t) to enhance seismic signal and suppress seismic noise. This results in a signal which is scaled up in amplitude in the presence of seismic signal and scaled down in amplitude in the presence of seismic noise, which signal I call the signal-enhancement-function signal.
  • the signalenhancement-function signal is half-wave rectified and then multiplied by the original vertical geophone signal, V, (t), which has been stored by any appropriate means.
  • This second product signal may then be bandpass filtered to attenuate undesired frequencies, which are the frequencies higher than those of seismological interest, the typical upper limit of which might be, for example, 40, 60 or '70 l-Iz., depending on the formation under investigation.
  • the resulting signal is one in which seismic signals have been significantly enhanced, seismic noise has been significantly attenuated, and undesired frequencies have been removed.
  • the data center would include a multiplier 14, into which the recorded outputsignals from the horizontal and vertical geophones are fed, and which forms the product V, (t) V, (t) as its output signal.
  • This output signal is then applied as the input to a positive halfwave rectifier 15.
  • the output of rectifier and the vertical geophone output signal, V, (t), which has been stored in recorder 13, are applied as input signals to a second multiplier 16, the output of which is applied as the input to a band-pass filter 17 to attenuate undesired frequency components, as previously mentioned.
  • the particular construction of analog recorders l2 and 13, multipliers l4 and 16, rectifier 15 and filter 17 are well known to persons skilled in the art, and no novelty is asserted for the individual components of this analog system. The combination of these elements, however, is suggested only by the discoveries and analyses described herein.
  • the signal-enhancement-function signal, V, (t) V, (t) is supplied to a polarity-sensing device, such as a simple switching circuit, which will produce an output signal only when the signal-enhancement-function signal is positive.
  • This output signal may then be used to trigger a gate, the input to which is the above-mentioned output of the vertically oriented geophone.
  • all portions of the signal V, (t) occurring when the signal-enhancement-function signal V, (t) V, (t) is not positive are eliminated.
  • the resulting signal in which noise has been attenuated and signal been enhanced, may then be filtered as above to eliminate frequencies outside the range of seismological interest.
  • FIG. 5 of the drawings apparatus for carrying out this technique is schematically shown.
  • Components 10, ll, 12, 13 and 14 function as stated above with respect to FIG. 4.
  • the output of multiplier 14 is applied to a polarity-sensing device 18, such as a simple electronic switch or a relay, which is set to produce an output signal only when the input signal is positive.
  • the output signal from the polarity sensor 18 is then applied as the control signal to a suitable gate 19, the input to which is the signal from the vertically oriented geophone, V, (t), which has been stored in the second analog recorder channel 13.
  • the gate 19 is set to produce an output signal only when the control signal from polarity sensor 18 is present.
  • the output of the gate 19 is then applied to band-pass filter 17 to remove undesired frequency components, as above described with reference to FIG. 4.
  • the output signals of the gate 19, and of filter 17, have an improved ratio of seismic signal to seismic noise, as compared with the output of the vertically oriented geophone 5 as shown in FIGS. 2 and 3.
  • the methods above described can be carriedout with equipment other than the described thus far.
  • the recording equipment could be digital, such as the Texas Instruments Model 10,000 Digital Field System, as opposed to analog, and the succeeding steps could be carried out on any general-purpose digital computer.
  • signals representative of the functions V, (t) and V, (I) may be produced by arrays of horizontally oriented and vertically oriented geophones, as known in the art and described in the article by C. H. Savit,,l. T. Housead and J. Sider,.entitled The Moveout Filter," in Geophysics, vol. XXIII, no. 1, January 1958.
  • V, (t) V, (t) may be employed to improve signal-to-noise ratio in ways other than those specifically described herein.
  • a seismic data processing method comprising the steps of:
  • a method of processing seismic signals in the presence of seismic noise comprising the steps of:
  • first and second signals respectively representative of waves received from a generally horizontal direction and a generally vertical direction
  • a method of processing signals representative of geophysical data comprising the steps of:
  • first and second signals respectively representative of waves received from a generally horizontal direction and a generally vertical direction
  • Apparatus for processing seismic signals in the presence of seismic noise comprising;
  • a second geophone mounted so as to be principally sensitive to energy received from a vertical direction
  • first multiplying means for multiplying the output signal of said first geophone by the output signal of said second geophone
  • second multiplying means for multiplying the output of said half-wave rectifying means by the output of said second geophone
  • Apparatus according to claim 12 further comprising means for recording the output signals of said first and second geophones.
  • a seismic data processing method comprising the steps of:
  • Apparatus for processing seismic signals in the presence of seismic noise comprising:
  • a second geophone mounted so as to be principally sensitive to energy received from a vertical direction
  • Apparatus according to claim 17, further comprising means for recording the output signals of said first and second geophones.

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  • Engineering & Computer Science (AREA)
  • Remote Sensing (AREA)
  • Physics & Mathematics (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Acoustics & Sound (AREA)
  • Environmental & Geological Engineering (AREA)
  • Geology (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Geophysics (AREA)
  • Geophysics And Detection Of Objects (AREA)
  • Noise Elimination (AREA)
US00178654A 1971-09-08 1971-09-08 Method and apparatus for increasing seismic signal-to-noise ratio Expired - Lifetime US3736556A (en)

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3858168A (en) * 1972-09-13 1974-12-31 Petty Ray Geophysical Inc Method of filtering multi-component seismic data
US4300220A (en) * 1980-05-16 1981-11-10 Phillips Petroleum Co. Three component detector and housing for same
US5007031A (en) * 1988-12-30 1991-04-09 Union Oil Company Of California Apparatus for positioning geophones in shallow holes
US5307325A (en) * 1992-08-31 1994-04-26 Magnavox Electronic Systems Company Accelerometer sensor noise reduction method and means

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2446494A1 (fr) * 1978-12-11 1980-08-08 Geophysique Cie Gle Dispositif et procede pour l'enregistrement de donnees sismiques
US4534020A (en) * 1981-10-19 1985-08-06 Phillips Petroleum Company Apparatus and method for detecting seismic waves

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
Seismic Signal Enhancement With Three Component Detectors, Shimshoni and Smith, Geophysics, Vol. XXIX, No. 5, pp. 664 671. *

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3858168A (en) * 1972-09-13 1974-12-31 Petty Ray Geophysical Inc Method of filtering multi-component seismic data
US4300220A (en) * 1980-05-16 1981-11-10 Phillips Petroleum Co. Three component detector and housing for same
US5007031A (en) * 1988-12-30 1991-04-09 Union Oil Company Of California Apparatus for positioning geophones in shallow holes
US5307325A (en) * 1992-08-31 1994-04-26 Magnavox Electronic Systems Company Accelerometer sensor noise reduction method and means

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GB1339530A (en) 1973-12-05
FR2152549A1 (https=) 1973-04-27
FR2152549B1 (https=) 1976-05-21
AU4257672A (en) 1973-11-29

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